This is an attempt to deal with one of the crucial problems in modern medicine: the rapid rate of exchange of truths serving as the foundation of medical practice. Unstable truths are a source of scepticism and concern among many physicians. They are also one of the main reasons for the crisis undermining the trust between patient and physician. The quest for the truth in modern medicine passes through the six core concepts of scientific truth: paradigms, methods, borders, criteria, interpretation and inference. The author deliberates each of these concepts through concrete examples at three levels: the historical, the theoretical and the political. The issues serving as the basis of the discussion are of concern to the medical world, and appear at the core of professional and sometimes the public debate: management of coronary heart disease, treatment of bronchial asthma, hormone replacement in menopausal women, early detection of breast cancer, drug therapy for diabetes, conventional versus alternative medicine.